In a few months, I will be performing for at a very large event. I would like my fun piece to not only sound great, but be entertaining to watch as well. Do you have any advice on how to work with the audience when performing (regarding facial expressions, etc.)? Is there any special "choreography" that I should take note of when performing a piece (for example, lifting hands off the piano at a certain time when the piece is done)? Do you know any resources that I could use to aide me in the process? Your advice is greatly appreciated!
I would never endorse facial expressions or choreography unless the music demands it. There's nothing worse than watching a pianist artificially throw their limbs into the air because they think it may entertain the audience.
I suggest you start at the root of the issue vs. its surface. Instead of asking what sorts of gimmicks and tricks you can utilize to "entertain" the audience, ask yourself how you can heighten the impact of the music. Most of your energy should go straight back into the music itself; you should be performing every piece as if it's the last time anyone in the world will ever listen to it.
Only after you've uncovered exactly what makes the music tick will other facets of the performance become clear. If for some wild reason, you end up tossing a sexy glance to the audience, it will be because you had no choice but to toss a sexy glance to the audience. It will be something the music demands of you; not something you decided to do because you thought it would be cute. Likewise, your outfits should be dictated by your interpretation of the music and not by whichever outfit may generate the biggest gasp from your audience.
Sabre Dance or A New Account of the Blue Danube Fantasy are unusual because they demand some visual performance as well as musical, but in most pieces you'll find that contorting your face and flailing your limbs are unnecessary and artificial. In the end, if you do your job, if you do what the music demands of you, you will entertain your audience.